1. Field of the Invention
The present invention relates to a masking material to be used in the photomechanical process when a proof is made on a color paper and similar materials, with unnecessary parts masked.
2. Description of the Prior Art
Conventional masking materials used in the photo-mechanical process are mostly applicable only to ortho-chromatic materials which are sensitive to the regions of the spectrum up to about 580 nm. (See Japanese Patent Laid-open Nos. 143758/1986 and 314553/1988 and Japanese Patent Publication No. 46011/1983). Although there are a few kinds of masking materials that can be applied to photosensitive materials having a broader range of spectrum than orthochromatic materials, they are extremely hard to work with.
At present, the masking of color papers and similar materials (which are sensitive to all the wavelength of visible light) is achieved by using a thick masking material having an extremely low transmittance or by using two or more kinds of masking materials which are different in the wavelength of light they transmit. The former case has a disadvantage that the masking material with an extremely low transmittance makes the underlying original nearly invisible even though a light table is used, and the thick masking material is difficult to cut. The latter case also has a disadvantage that it is very difficult to cut exactly and neatly two or more masking materials placed one over another.
It is common practice in the photomechanical process to make proofs on color paper, and the masking material for this purpose should permit easy cutting on a light table, with the underlying original clearly visible, and yet shut out the light to which color paper is sensitive. However, none of the conventional masking materials meet these requirements.